1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for an image pickup apparatus using a solid-state image pickup element, such as a video camera, an electronic still camera, a broadcasting camera, and a monitor camera, or an image pickup apparatus such as a silver-halide film camera.
2. Description of the Related Art
In recent years, a zoom lens which has a short total lens length, a compact size, a high zoom ratio, and a high resolving power has been requested for an imaging optical system used in an image pickup apparatus. A positive lead type zoom lens in which a lens unit having a positive refractive power is arranged closest to an object is known as a zoom lens which responds to those requests. As the positive lead type zoom lens, there is known a zoom lens which is constructed of five lens units as a whole.
In Japanese Patent Application Laid-Open No. 2007-178598 and Japanese Patent Application Laid-Open No. 2007-178769, there is disclosed a zoom lens which includes first to fifth lens units having positive, negative, positive, positive, and negative refractive powers and being arranged in order from an object side to an image side, and which carries out zooming by moving the second lens unit and the fourth lens unit, and carries out focusing by moving the fourth lens unit.
In a zoom lens in general, in order to realize the downsizing of the entire system while the high zoom ratio is ensured, it is only necessary to reduce the number of lenses while increasing the refractive powers of the lens units constructing the zoom lens.
However, in the zoom lens structured in such a manner, a lens thickness increases with an increase in the refractive power of each of the lens surfaces, and an effect of shortening the lens system becomes insufficient. Further, at the same time, various aberrations are frequently generated, and hence the satisfactory correction for the various aberrations becomes difficult to carry out. Thus, the high optical characteristic becomes difficult to obtain.